Interpretive Summary: Varroa mites are an external parasite of honey bees and the most serious threat to the the survival of colonies. New methods are needed to control this pest because the mites have become resistant to some registered miticides, and other control methods are either not consistently effective or harm brood and bees. One group of compounds that has not been examined for their effects on Varroa mites are beta acids from hop plants. These compounds reduce feeding and egg laying behaviors in certain plant feeding mites. We tested their effects on Varroa mites and bees using topical applications of the compounds and by saturating cardboard strips with the beta plant acids and putting them in colonies and in packages of bees. Concentrations of 1% or less beta plant acids applied directly to newly emerged worker bees caused minimal mortality after 21hours. When Varroa were placed on those bees, there was 100% mite mortality. In colonies, mite drop lasted for about 7days after application of the saturated strips with the highest drop occurring in the first 2-3 days after treatment. Bee and queen mortality in the colonies was not affected by treatments. When cardboard strips saturated with beta acids were put in packages of bees, more than 90% of the mites were killed without an increase in bee mortality. Using beta plant acids from hops appears to have potential to control Varroa when establishing colonies from packages or in hives during broodless periods.

Technical Abstract:
Beta acids from hop plants (Humulus lupulus L.) reduce feeding and oviposition behaviors and increase mortality in certain phytophagous mites. These compounds were tested for their effects on Varroa destructor (Anderson and Trueman) mortality. The effects of hops beta acids (HBA) on honey bee (Apis mellifera L.) mortality also were tested. Concentrations of 1% or less HBA diluted in polyethylene glycol applied directly to newly emerged worker bees caused minimal mortality after 21hours. When Varroa were placed on those bees with topical applications of 1% HBA, there was 100% mite mortality. Cardboard strips saturated with HBA and placed in colonies resulted in mite drop that was significantly greater than in untreated colonies. HBA was detected on about 60% of the bees in colonies during the first 48hrs after application. Mite drop in colonies lasted for about 7days with the highest drop occurring in the first 2-3 days after treatment. There was a reduction in the percentages of bees with HBA and in the amounts on their bodies after 7 days. Bee and queen mortality in the colonies was not affected by HBA treatments. When cardboard strips saturated with HBA were put in packages of bees, more than 90% of the mites were killed without an increase in bee mortality. Using HBA appears to have potential to control Varroa when establishing colonies from packages or during broodless periods.